Auto gearbox problem

[willyworm]

I have Volvo v70 diesel, with an auto gearbox. It has done over 200K miles. The gear change is irrational and it changes gear when it should not do so! I have been told that it is not a faulty gearbox but something to do with a selector valve. Can anybody enlighten me to what the problem is? I don't want to scrap the car as everything else is OK and I also don't want to spend a lot of money either, Thanks.

[lgw]

When did it last have the gearbox oil and filter changed ??